Black bird with white belly and under wings?

The bird you are describing sounds like it could be a Black-capped Chickadee or possibly a type of blackbird like the Common Grackle. Both have dark plumage with lighter underparts, but the specific identification may depend on other features such as size, habitat, and behavior. If you're observing it in a specific region, that can also help narrow down the possibilities. For a precise identification, consider consulting a local bird guide or app.